Dense sampling of ethnic groups within African countries reveals fine-scale genetic structure and extensive historical admixture by Bird, N, Ormond, L, Awah, P, Caldwell, EF, Connell, B, Elamin, M, Fadlelmola, FM, Matthew Fomine, FL, López, S, MacEachern, S, Moñino, Y, Morris, S, Näsänen-Gilmore, P, Nketsia V, NK, Veeramah, K, Weale, ME, Zeitlyn, D, Thomas, MG, Bradman, N, Hellenthal, G